I have a rewire to do in a couple of weeks and the house has plaster walls and ceilings. The AHJ tells me that I will have to add recepts where they currently are not and that means a lot of new holes. I need to know of a good way to cut these holes without cracking the plaster . I don't think that a sawsall would be very gental but a keyhole won't work either.
Any ideas?
Chris

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I use the Dewalt cordless “RotoZip” style tool with an 1/8” tile cutter bit to cut the outline of the box in the plaster, then switch to the standard wood cutting spiral bit to cut through the lath. If the plaster is over a heavier backing, like 3/4” tongue and groove board, I use a cordless jigsaw or reciprosaw for the second step. I use a couple of layers of blue painters tape around the outline of the box to prevent the shoe of the tool from scratching the surrounding area.If you don’t already have them, I would also recommend the 9/16” X 54” Diversibits for drilling through cross blocking that seems to be prevalent in old non-standardized construction. If you have the cash and are going to do a lot of this kind of old work, the Rigid SeeSnake Micro is also unbelievably handy for peering into otherwise inaccessible spaces.

I use the Dewalt cordless “RotoZip” style tool with an 1/8” tile cutter bit to cut the outline of the box in the plaster, then switch to the standard wood cutting spiral bit to cut through the lath. If the plaster is over a heavier backing, like 3/4” tongue and groove board, I use a cordless jigsaw or reciprosaw for the second step. I use a couple of layers of blue painters tape around the outline of the box to prevent the shoe of the tool from scratching the surrounding area.If you don’t already have them, I would also recommend the 9/16” X 54” Diversibits for drilling through cross blocking that seems to be prevalent in old non-standardized construction. If you have the cash and are going to do a lot of this kind of old work, the Rigid SeeSnake Micro is also unbelievably handy for peering into otherwise inaccessible spaces.

I have found by trial and error that the cheap Mikita 9.6 volt jig saw cuts the lath perfectly without shaking it loose as a more powerful saw like the 18v DeWalt will do.
I second the see-snake and diversibits, they make the job much easier.

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Just cut a bunch of boxes into some 100 year old horsehair plaster. I used my dremel tool with a fine cutting wheel to score the plaster, removed it, and a spiral bit to cut the lath. Worked great, except the spiral bit got that old lath to smoking a bit. Then a piece fell into the hole and down into the wall where it sat and smoked for a while. A couple of squirts from my trusty fire extinguisher, and all was well.

The kind of plaster makes a difference. There is hard stuff and soft material that seems to be as much animal hair or other filler as it is plaster.

It is often easier to use a wood chisel and mallet to tap an outline in the soft material then remove the material inside the outline with light taps on the chisel. Then the lath can be cut - I usually use a very fine tooth in a sabre saw as the plaster will destroy a Roto-Zip bit or 2 per opening. Usually I only make vertical cuts and break out the pieces on the top and bottom of the upenings if necessary. A little research can often get a height above floor distance that will let you cut out 1 full lath piece and 2 partials which leaves these soft walls with the best support. Almost any vibration will destroy significant amounts of plaster in these walls - don't hurry.

In hard plaster I generally tap the outline with a chisel then go after it with the Roto-Zip.

Plaster seems to be a bit different in every house. Do the first few very carefully and see how the plaster reacts to what you're doing. And, I'd second (third?) the other advice.

There's pretty good money in this if you can get a reputation for being able to work in plaster walls without tearing them up.

The Following User Says Thank You to itsunclebill For This Useful Post:

Just cut a bunch of boxes into some 100 year old horsehair plaster. I used my dremel tool with a fine cutting wheel to score the plaster, removed it, and a spiral bit to cut the lath. Worked great, except the spiral bit got that old lath to smoking a bit. Then a piece fell into the hole and down into the wall where it sat and smoked for a while. A couple of squirts from my trusty fire extinguisher, and all was well.

Receps turned out great.

Fire has always been on my mind with the rotozip cutting. What if it was smouldering and you didn't know and it got worse after? I think the slower the better with this old stuff. A metal blade in the little Makita is perfect, never made a mess so far. I agree that plaster composition differs with each house, sometimes just room to room. I find that 3M wall repair compound works wonders for patching the old stuff quickly in one application.

__________________A Veteran - whether active duty, retired, guard or reserve - is someone who, at one point in his life, wrote a blank check made payable to "The United States of America," for an amount of "up to and including my life."

Fire has always been on my mind with the rotozip cutting. What if it was smouldering and you didn't know and it got worse after? I think the slower the better with this old stuff. A metal blade in the little Makita is perfect, never made a mess so far. I agree that plaster composition differs with each house, sometimes just room to room. I find that 3M wall repair compound works wonders for patching the old stuff quickly in one application.

This stuff was so deteriorated it crumbled easily, but the cutting wheel did the trick.

This whole job was a pain. My electrician had gone over to do the work, got 3/4 done and actually walked off the job. The customer was difficult, to say the least. In fact, beyond difficult..way beyond. I ended up finishing the job myself, doing some extra work for free, and paying a painting contractor to repair the plaster my electrician's helper had messed up.

Anyway, at the end of the day the customer was satisfied, (as satisfied as she will ever be) and I didn't lose any money, I just didn't make much. I could tell at the walk through she would be trouble, so I loaded the price right up. Not quite enough as it turns out, but at least we didn't get hurt.

RK, after the smoking lathe incident, I used my sawzall with a fine metal bit to cut the wood. Not as good as a jigsaw, but it worked. My brother borrowed my jigsaw.

I could tell at the walk through she would be trouble, so I loaded the price right up. Not quite enough as it turns out, but at least we didn't get hurt.
.

Working for a PIA is bad, doing it while it costs you for the time is the worst.

__________________A Veteran - whether active duty, retired, guard or reserve - is someone who, at one point in his life, wrote a blank check made payable to "The United States of America," for an amount of "up to and including my life."

Just cut a bunch of boxes into some 100 year old horsehair plaster. I used my dremel tool with a fine cutting wheel to score the plaster, removed it, and a spiral bit to cut the lath. Worked great, except the spiral bit got that old lath to smoking a bit. Then a piece fell into the hole and down into the wall where it sat and smoked for a while. A couple of squirts from my trusty fire extinguisher, and all was well.

Receps turned out great.

I've melted the blades on that old plaster lathe before. Its tough stuff!!

I use a rotozip on just about every job, reworking old houses in plaster, sheetrock, and widening old outlet holes in baseboards. The real bear is some of the old metal strapping that holds old boxes in place where you have to come behind with the sawsall.

You just have to make sure when you start a new box that you aren't running up against a stud and leaving a hole you can't cover in the plaster. Drill a pilot, with the rotozip or a drill, and use a piece of wire to spin in the hole and make sure your wall is deep enough and wide enough for your box, making sure there isn't anything in the way.

The only time i find the smoking/fire hazard seems extreme... maybe if you are running against paper from fiberglass insulation... or working with a dull bit. You can alway control the depth of your cuts, and do several to reduce the heat and smoldering. Got to get good freehanding the rotozip though. Relying on the depth cutter is lame... Brand new bits can get away from you in softer material. Best to hold the sucker with two hands... and use safety glasses with that plaster. Especially cutting over your head.

Oh yeah and sometimes there is that nasty metal wire mesh behind there. Tin-snips and a metal file and a lot of plunging around through the tiny holes.

Take some blue painters tape and mark of your openings I always use a cordless roto zip get some one with a steady hand to cut the holes otherwise the wall might look like some wrote something in cursive.

Some plaster walls have wire mesh or wood lathe behind.
wire mesh will eat through most blades fast a carbide blade will work best with plasters

Also the makita mini circular saw with carbide blade will cut through pretty much anything.